1. Field of the Invention
The field of invention relates to fastener structures and more particularly for a lightweight plastic fastener utilized in the aircraft industry which replaces a conventional bolt/screw-and-nut combination. Typically fasteners retain two or more elements together with a varying grip range. In aircraft applications it can be used to attach small diameter tube-clamps, guide blocks and cushion clamps. There are many applications where steel bolts/screws are structurally excessive and therefore overweight. The fastener of the present invention is installed with a squeezing or a push-pull motion rather than torsional rotation as used with conventional screws and bolts.
2. Description of the Prior Art
Plastic fasteners of various types have been well known in the prior art for a variety of different uses, such as binding a series of pages in a book-like form in a rapid manner, as typified in Tanaka, U.S. Pat. No. 5,074,696 which teaches a fastener used in binding pages:
Plastic wire tie fasteners are well known in the art which utilize a somewhat similar structure to the present invention to bind a bundle of wires. The flexible stem of the wire tie includes a longitudinal rack of serrated teeth that are pulled through an aperture having a deflectable locking tab which ratchets the teeth on the flexible stem to retain a bundle of wires together.
The patent to Vian, U.S. Pat. No. 3,938,587, illustrates a plastic tension fastener with a conventional male/female relationship between a bolt and nut which has a limited contact area between the latching teeth 26 on the nut and the cogs 30 on the bolt.
The patent to Sun et al, U.S. Pat. No. 4,730,972 teaches another fastener assembly for binding paper sheets in a conventional male/female relationship between the two binding parts 20 and 12 having mating teeth thereon which ratchet together.
The fastener of the present invention joins two or more elements together in a bolt like fashion whereby a pair of identical fasteners in opposed relationship are engaged together wherein the stem of one, which is semicircular in cross-section, is inserted through an aperture in the head of the other whereby a rack of serrated teeth on the inside flat surface of each stem is engaged by deflectable locking tabs attached to the opposite fastener. A dual ratcheting function is provided so each fastener engages and holds the stem of the other fastener so if one locking tab failed the fasteners would remain engaged to each other by reason of the locking tabs on the other fastener.
Once applicant""s fastener has engaged what it is attempting to hold, the extending portions of the stem are cut off leaving a bolt like fastener custom sized to grip length with similar heads on opposite ends of the bolt. Due to the original length of the stem portions, the fastener has a variable grip length with a range between 0.05 inches and 1.75 inches. Larger sized fasteners could have greater grip lengths. The installation time with this fastener is very short due to the strictly lineal movement of the mating fasteners which can be engaged by either tensile action pulling the extending stems with a modified Panduit type wire tie gun. Also a compression action can be used by forcing the two heads together A whereby the locking tabs on each fastener ratchet along the rack of serrated teeth of the opposing fastener so as to firmly grip the items being joined.
The plastic fasteners of the present invention are substantially lighter than conventional bolts or screws. Removal of the fastener of the present invention is quickly removed by merely cutting off one of the heads through the center of the head.
The fastener of the present invention is used in pairs which are engaged in opposite juxtaposed orientation to each other wherein the stems of each fastener are inserted through a semi-circular aperture in the head of the opposing fastener whereby locking tabs within each head engage the serrated teeth positioned longitudinally along the flat diameter surface of the stem of the other in a ratcheting manner with each fastener providing an engagement means with the other.
The previously mentioned patent to Tanaka is similar to the present invention in that it utilizes a pair of fasteners placed in opposite orientation to each other wherein a rack of serrated teeth positioned on the diameter surface of each fastener engages a similar series of serrated teeth on the opposite fastener to provide a bolt-like tension fastener assembly. The two identical fasteners are held in juxtaposed coaxial relation by means of a pair of rigid plates 18 and 19 which are separate and apart from the fasteners. The Tanaka fasteners can accommodate a varying grip range. However, it is limited in that the pair of fasteners cannon overlap past the head of the fastener, which is contrary to the present invention. Also, the two plates, which the Tanaka fasteners pass through, must have a relatively large tolerance fit since the unmeshed depth of the serrated teeth require a larger diameter hole.
It is therefore the principal object of the present invention to provide a variable grip range fastener used in pairs having a dual set of locking teeth.
A further object of the present invention is to provide a fastener with a smooth circular shank once assembled with its clearance hole.
Another object of the present invention is to provide a single size fastener which provides a variable grip length which can be trimmed to a tailored configuration:
Another object of the present invention is to provide a fastener with a quick installation time wherein the manner of engagement is either tensile action or compression of the heads of the two fasteners.